Electrode arrangement

ABSTRACT

An electrode arrangement ( 10 ) comprises a knitted electrically conductive electrode portion ( 12 ) containing electrically conductive yarn and at least one portion ( 14 ) of moisture impermeable electrically conductive material attached to the electrode portion ( 12 ). During use the electrode portion ( 12 ) and portion of material ( 14 ) are applied to a wearers skin. The moisture impermeable material portion ( 14 ) is of silicon loaded with carbon black. The moisture impermeable portion ( 14 ) encourages perspiration of a user and the perspiration trapped between the skin and moisture impermeable portion ( 14 ) reduces skin to electrode contact resistance to increase efficiency of detection of user heart rate or other electrical signals generated by a user.

The present invention relates to performance improvements insubstantially fabric based electrodes.

WO-A-01/02052 relates to a garment comprising at least two zones; onebeing formed of electrically insulative yarns and the other being formedof one or more electrically conductive yarns. The zone comprisingelectrically conductive yarns is intended to function as an electrodesurface for contacting the corpus. Therefore the zone comprisingelectrically conductive yarns is present on the inner side of thegarment, which is to contact the corpus skin. WO-A-01/02052 states thatan electro-conductive gel can be used between the zone containing theelectrically conductive yarns and the skin to assist the electricalcontact between yarn and skin. It is not always desirable to introducesuch gel between an electrode and the skin for a number of reasons, butin any case people are not always happy to apply a liquid or gel to afabric based article.

Trials conducted with a textile based electrode (of which the electrodeof WO-A-01/02052 is an example) fitted to a wearer have shown that theelectrical resistance between the conductive portion of the textilebased electrode and the skin of a wearer to which the electrode isapplied is high enough to render detection of electrical signalscorresponding to the wearers heartbeat very difficult. These signals areof the type that can be used to generate an electrocardiogram. Thedifficulty in detecting these electrical signals is not helped whenthere is an upper limit on the percentage of electrically conductivematerial that can be present in the electrode conductive portion, eitherfor reasons of limitations imposed by the manufacturing process orbecause the feel or other physical property of the conductive portionwould be adversely affected.

It is an object of the present invention to provide a substantiallyfabric based electrode arrangement with improved performance incomparison with a fabric based electrode not benefiting from the presentinvention.

In accordance with a first aspect of the present invention there isprovided a fabric electrode arrangement exhibiting a first surface forapplication to the skin of a mammal, wherein said fabric electrodearrangement comprises at least one portion of material beingsubstantially impermeable to moisture, said material being located onsaid first surface.

Because the at least one portion of material is substantiallyimpermeable to moisture, the act of placing that material on the wearersskin would restrict the amount by which the skin underneath is able tobreath. During use of the electrode arrangement, the at least oneportion of material is positioned on the wearers skin which promotesgathering of perspiration between the skin and the portion of materialby virtue of restricting the degree to which that skin is able tobreath. A person secretes moisture from their skin naturally butmoreover when a person takes exercise the exertion causes a person toperspire and the at least one portion of material traps perspirationbetween itself and the skin. The presence of the moisture orperspiration reduces the electrical resistance present between the skinand portion of material and so in turn reduces the electrical resistancepresent between the skin and electrode arrangement. The reduction inelectrical resistance allows more efficient detection of electricalsignals that may be associated with the body of a wearer, such aselectrical signals corresponding to the heartbeat of the wearer, whichmay be used to produce an electrocardiogram. The increased efficiency ofdetection has the potential to allow more reliable measurement of theelectrical signals under a wider variety of conditions thereforeimproving reliability of measurement, facilitating the measurement ofsignals in circumstances where it would otherwise not be possible toperform successful measurement, or allowing use of less sensitive lowercost measuring apparatus.

In cases where the electrode arrangement is to be used in or inconjunction with fitness measuring equipment, sports training aids,exercise equipment or other such equipment where a user will undergophysical exertion, the electrode of the present invention willcontribute to more efficient detection of user signals, especiallyduring the early stages of exertion. Tests have revealed that a basicknitted electrode of the type generally described by WO-A-01/02052 doesnot perform as well during early stages of user activity but performsmuch better once a user begins to perspire appreciably, therebymoistening the basic electrode and reducing the electrical resistancebetween the basic electrode and the wearers skin. Therefore, in caseswhere the electrode arrangement is to be used for monitoring a patientwho is not exercising, the electrode arrangement of the presentinvention provides detection of user signals when the basic knittedelectrode of the type generally described by WO-A-01/02052 may not.

Furthermore, the applicants have found that fabric based electrodes canexhibit electrical noise when distorted as can occur during stretchingor bending of the fabric electrode. In the case of the electrode of thepresent invention, the increased efficiency of detection of electricalsignals made possible by promoting reduction of the resistance betweenthe skin and electrode arrangement helps to avoid or reduce the effectsof such noise causing undesirable masking of the users electricalsignals or otherwise interfering with the detection of such signals,which latter case can confuse signal processing apparatus.

Optionally, said at least one portion of material is located directly onsaid first surface. Otherwise, one or more intermediate layers offurther material may be present between the one portion and said firstsurface.

Optionally, said at least one portion of material can be bonded to saidfirst surface. Bonding may be performed with or without the addition offurther bonding material.

Preferably, the material is mechanically flexible. Thus, the at leastone portion of material is able to flex in sympathy with the firstsurface of the electrode arrangement.

The said material may exhibit a resistivity of less than 500 ohms persquare.

However, an important property is the electrical resistance across thethickness of the material, that is the dimension between the surface forcontacting the users skin and the surface for contacting the firstsurface of the fabric electrode. Ideally this resistance is as low aspossible but a value of a few 10's of Ohms to a few hundred Ohms istolerable. Typically the thickness is in the order of a few mm.

In one optional implementation, said material is silicone rubber loadedwith conductive material. The conductive material can be carbon black orsilver powder.

In a preferred arrangement, the at least one portion or a plurality ofsuch portions collectively occupy a proportion of between one fifth andone half inclusive of that area of the first surface intended to beapplied to the skin.

In general it is desirable that the presence of the at least one portionof material or plurality of such portions does not detract from theinherent advantages of a fabric electrode; these include the electrodebeing flexible, mechanically elastic and allowing the wearers skin tobreathe thereby contributing to user comfort. In respect of this lastadvantage, the at least one portion of material reduces the ability ofthe skin to breath so the area of the first surface occupied by theportion or portions of material needs to be chosen to strike a goodbalance between providing an electrode arrangement which generallyallows the skin to breath but which promotes gathering of perspirationin specific regions to reduce electrical contact resistance between theskin and electrode.

The said electrode can be of a knitted construction or a wovenconstruction. Thus by choice of appropriate materials the electrode canbe made comfortable for a user to wear and also permits a fair degree ofbreathing of the skin covered by the electrode.

The said electrode can be integral with a garment which permits thegarment and electrode to be mass produced in a cost-effective manner.Furthermore an electrode that is integral with a garment also permitslow profile or more elegant structures to be realised.

In accordance with second aspect of the invention there is provided asubstantially textile article comprising the fabric electrodearrangement.

In accordance with a third aspect of the present invention there isprovided a wearable article comprising the fabric electrode arrangement.

In accordance with a fourth aspect of the present invention there isprovided a garment comprising a fabric electrode arrangement exhibitinga first surface for application to the skin of a mammal, wherein saidfabric electrode arrangement comprises at least one portion of materialbeing substantially impermeable to moisture, said material being locatedon said first surface.

These and other aspects of the present invention appear in the appendedclaims to which the reader is now referred and which are incorporatedherein by reference.

The present invention will now be described with reference to theFigures of the accompanying drawings in which:

FIG. 1 shows a first embodiment of an electrode arrangement made inaccordance with the present invention;

FIG. 2 shows a schematic arrangement of an electrode arrangement of thepresent invention positioned on a wearer and electrical resistancemeasuring equipment;

FIG. 3 shows plots of electrical resistance measured across twoelectrodes of an electrode arrangement placed in contact with a wearersskin; and

FIGS. 4 a-4 c show further embodiments of an electrode arrangement madein accordance with the present invention.

It should be noted that the drawings are diagrammatic and not drawn toscale. Relative dimensions and proportions of parts of the figures havebeen shown exaggerated or reduced in size for the sake of clarity andconvenience in the drawings. The same reference signs are generally usedto refer to corresponding or similar features in the differentembodiments.

The first illustrated embodiment of a fabric electrode arrangement 10 isshown located on a textile article 11 (part shown), the electrodearrangement including an electrically conductive electrode portion 12exhibiting a first surface 13 and a portion of material 14 located onthe first surface 13. The first surface 13 and the material 14 areintended to contact the skin of a wearer during electrode use. Theportion of material 14 is substantially impermeable to moisture and iselectrically conductive. In this example the portion of material 14 isof silicon rubber loaded with carbon black. The portion of material 14is 1.2 mm thick, has a surface area of 0.035 m² for presenting to thewearers skin during electrode use and exhibits an electrical resistanceof 120 Ohms per square.

Ideally, the resistance measured across the thickness of the portion ofthe material 14 should be as low as possible but may be in the order of10's of Ohms or lower, but ideally less than 200 Ohms or so. Bythickness it is meant that dimension between the surface of portion 14which contacts the wearers skin and the surface of portion 14 whichcontacts the first surface 13 of conductive electrode portion 12.

The electrically conductive electrode portion 12 is of knittedconstruction. More specifically the first embodiment is of plain knitstructure using yarn comprising tactel™ (a type of nylon) which is anelectrical insulator and stainless steel which is an electricalconductor. The yarn is a staple yarn and comprises 20%-30% of thestainless steel. As illustrated in FIG. 1, the yarn is knitted to extendin the direction denoted x.

The electrical resistance of the conductive electrode portion 12 whenmeasured lengthways over distance denoted d₁ in FIG. 1 is in the regionof 20 Ohms to 40 Ohms but in any case in the region of 10's of Ohms.Distance d₁ is 0.065 m.

The need to reduce the electrical resistance between the users skin andthe conductive electrode portion 12 could be met to some extent byincreasing the percentage of conductive material in the electrodeportion 12. This could be done by increasing the percentage of stainlesssteel in the yarn used to knit the electrode or by introducing a furtheryarn having conductive qualities. However, manufacturing constraints canimpose a limit on the amount of conductive material that can be includedin the knit. Furthermore, as the amount of conductive material isincreased the electrode portion 12 takes on a feel that is progressivelydissimilar to the textile article 11 that it is integrated with andbecomes less flexible and less comfortable when worn against the usersskin.

The electrically conductive electrode portion 12 may be sewn, glued orotherwise attached to the textile article 11. Alternatively theelectrically conductive electrode portion 12 may be an integral part ofthe textile article 11. In the latter case, where the textile article 11is of knitted construction the electrode portion 12 may also be ofknitted construction and formed during the same production processmerely by appropriate selection of electrically conductive yarn duringknitting of the article to define the electrode portion. Intarsia andjacquard techniques may also be used, or the conductive yarn may be“laid in”.

The portion of conductive moisture impermeable material 14 is attachedto the electrode portion 12 by suitable electrically conductive adhesivebut may be attached by other means such as heat bonding (partiallymelting: the impermeable material onto the electrode portion 12),ultrasonic welding, sewing or other means as will be appreciated by theperson skilled in the art. In certain cases the conductive properties ofmaterial 14 may permit attachment by inductive welding.

Measurement of the electrode to skin electrical contact impedance wasconducted using the setup shown schematically in FIG. 2. A garment inthe form of a fabric band 11 is worn around the chest of the torso andis provided with an electrode arrangement having two conductiveelectrode portions 12 such that when the band is worn correctly, oneelectrode portion 12 is positioned on one front side of a wearers chestand the other electrode portion 12 is located on the other front side ofthe wearers chest. Each electrode portion 12 is provided with a portionof material 14 (not shown) that is impermeable to moisture andelectrically conductive, as already described with reference to FIG. 1.The electrodes 12 are rectangular in shape each with a height of 0.02 mand a width of 0.065 m as viewed while the garment 11 is appropriatelyworn, for example as shown in FIG. 2. The shortest spacing between theelectrodes is 0.01 m which is denoted in FIG. 2 as d₂. Each electrodeportion 12 and moisture impermeable portion 14 is held in contact withthe wearers skin by the band 11 during measurement.

A first one of the electrode portions 12 was connected to onemeasurement lead of an inductance, resistance and capacitance (LRC)meter while a second one of the electrode portions 12 was connected toanother one measurement lead of the meter. A 120 Hz measurement signalwas applied to the electrode portions and the impedance across the twoelectrodes was measured. For the avoidance of doubt each electrode wasphysically separated from the another but both were placed in contactwith a different portion of the wearers skin.

The resistance component of the measured impedance is shown in FIG. 3;this measurement being total series resistance of a first electrodeportion 12 in contact with the users skin and a second electrode portion12 in contact with another part of the users skin. Assuming the majorcomponent of the impedance is present at the electrode-to-skininterfaces, and in comparison impedance within the body is low, anapproximate indication of the electrode-to-skin impedance of oneelectrode can be reached by dividing the measured values by a factor oftwo.

Graph 30 shown in FIG. 3 has a linear x axis of time in minutes and alogarithmic y axis of resistance in kilo ohms. The measurements werestarted once the electrodes had been attached to a wearer and theelectrical resistance component of the measured impedance is shown byplot line 31. As can be seen initial measured resistance was in theorder of 80 k Ohms failing to around 25 k Ohms after 5 minutes ofcontinual wearing, approximately 15 k Ohms after 10 minutes of wearingand levelling off at around 12 k Ohms after 20 minutes of wearing. Thesemeasurements were taken with the wearer sitting down and the reductionof resistance over time is due to moisture forming between materialportion 14 and the wearers skin to reduce the electrical resistance atthe component 14 and skin interface.

To form a comparison the same set-up of FIG. 2 was used with knittedelectrodes of the same type and dimensions but not having the component14 of moisture impermeable conductive rubber. The electrical resistancecomponent of the measured impedance is shown by plot line 32. In thiscase the measured resistance is much higher, in the order of 750 k Ohmsto 850 k Ohms for the first 15 minutes of use for which measurementswere available.

The reduced electrical resistance or impedance of the electrodearrangement 10 improves the process of detecting electrical signals froma wearers body. The improvement is realised because during early stagesof wearing the electrode arrangement the formation of perspirationbetween the skin and the moisture impermeable material 14 reduceselectrical resistance between the skin and material 14. The electricalresistance between the material 14 and knitted conductive electrodeportion 12 is already low due to design of the electrode arrangement andso a path of relatively low electrical resistance is established betweenthe skin and conductive electrode portion 12 via the material 14. Thesaid path certainly has a lower electrical resistance in comparison withthe electrical resistance of a comparable direct skin-to-electricallyconductive textile portion 12 interface, especially when the wearersskin is dry. In fact, the nature of the knitted conductive electrodeportion 12 is such that it tends to absorb and dissipate userperspiration while letting the users skin breathe. While these effectscontribute to user comfort when wearing the electrode having a textileconductive electrode portion 12, they also raise the skin to electrodecontact resistance, at least until a wearer has performed enoughexercise to generate considerable perspiration to moisten the electrodeportion 12. Thus, the portions of electrically conductive material 14that are impermeable to moisture define regions of the electrodearrangement where a relatively low amount of perspiration serves toreduce electrode to skin electrical resistance.

Although electrical resistance between the users skin and fabric portion12 is quite high, the electrical resistance within electrode conductiveportion 12 is relatively low, that is in the region of 20 Ohms to 40Ohms when measured along length denoted d₁. Therefore, the combinedeffect of a conductive electrode portion 12 having a resistance of 10'sof Ohms and an impermeable conductive portion 14 having a resistanceacross its thickness of a few 10's of Ohms provides an efficientarrangement for detecting electrical signals of a user. By making themoisture impermeable portion 14 thin, efficiency can be improved and/ormaterials having a higher bulk resistivity can still be used to formportion 14.

Although the arrangement of the first embodiment is described with theportion of electrically conductive moisture impermeable material 14attached to the conductive electrode portion 12, the attachment does notneed to be direct and there may be one or more layer of electricallyconductive material between the material 14 and portion 12. Furthermoreattachment of the moisture impermeable material 14 to portion 12 is notmandatory because mere appropriate location of material 14, such thatduring use material 14 electrically contacts portion 12, either directlyor indirectly, is sufficient to allow operation in accordance with thepresent invention.

FIGS. 4 a-4 c show further embodiments of the present invention wherethe single circular portion of conductive moisture impermeable material14 has been replaced by other arrangements of such material. In FIG. 4 aelectrode portion 12 is provided with one or more substantiallyrectangular portions of conductive moisture impermeable material 14 a.In FIG. 4 b electrode portion 12 is provided with two or moresubstantially circular portions of conductive moisture impermeablematerial 14 b. In FIG. 4 c electrode portion 12 is provided with aplurality of circular portions 14 c of conductive moisture impermeablematerial, each of the portions 14 c being appreciably smaller in termsof the surface area they present to the users skin during use than thearea presented by portion 14 of the first embodiment shown in FIG. 1.However the or each portion 14 of electrically conductive moistureimpermeable material needs to be of a shape and size adequate toencourage the skin it covers to perspire; too small an area or toonarrow the portion and perspiration will not be encouraged and trappedin the manner required to reduce electrode to skin resistance asdescribed above.

While the present invention has been discussed with reference to aknitted electrode structure this is not a limiting feature of thepresent invention which has use in textile based electrodes in general,whether the electrodes are of a knitted, woven, embroidered, ornon-woven structure. Furthermore, although the present invention hasbeen described in the context of detecting signals from the body of awearer, the electrodes could also be used for application of electricalcurrent to a mammal.

In most cases the present arrangement will obviate the need for a userto actively wet an electrode component for correct operation. However,in some cases, depending on the user, it may be necessary to providesome supplementary moisture, for example by wetting the moistureimpermeable conductive portions 14. Even where such supplemental wettingis required, less moisture will be required to do this than would be thecase when wetting fabric portion 12 and the moisture impermeableportions are less prone to drying out than fabric conductive portions 12and so correct operation can be expected for a longer period than anarrangement without the impermeable conductive portions 14.

From reading the present invention other modifications will be apparentto persons skilled in the art. Such modifications may include otherfeatures which are already known in the design, manufacture and use offabric based electrodes, signal processing circuitry, garmentconstruction and materials and applications thereof and which may beused instead of or in addition to features already described herein.

1. A fabric electrode arrangement exhibiting a first surface forapplication to the skin of a mammal, wherein said fabric electrodearrangement comprises at least one portion of material beingsubstantially impermeable to moisture, said material being located onsaid first surface.
 2. An electrode arrangement in accordance with claim1 wherein said at least one portion of material is located directly onsaid first surface.
 3. An electrode arrangement in accordance with claim1 wherein said at least one portion of material is bonded to said firstsurface.
 4. An electrode arrangement in accordance with claim 1 whereinsaid material is mechanically flexible.
 5. An electrode arrangement inaccordance with claim 1 wherein said material is silicone rubber loadedwith conductive material.
 6. An electrode arrangement in accordance withclaim 5 wherein said conductive material is carbon black.
 7. Anelectrode arrangement in accordance with claim 1 wherein said materialexhibits a resistivity of less than 10,000 ohms per square.
 8. Anelectrode arrangement in accordance with claim 1 wherein the at leastone portion or a plurality of such portions collectively occupy aproportion of between one fifth and one half inclusive of that area ofthe first surface intended to be applied to the skin.
 9. An electrodearrangement in accordance with claim 1 wherein said electrode is of aknitted construction or a woven construction.
 10. An electrodearrangement in accordance with claim 1 wherein said electrode isintegral with a garment.
 11. A substantially textile article comprisingthe fabric electrode of claim
 1. 12. A wearable article comprising thefabric electrode of claim
 1. 13. A garment comprising a fabric electrodearrangement exhibiting a first surface for application to the skin of amammal, wherein said fabric electrode arrangement comprises at least oneportion of material being substantially impermeable to moisture, saidmaterial being located on said first surface.
 14. A fabric electrodearrangement, textile article, wearable article or garment substantiallyas described herein, with reference to or as illustrated in any one ormore of the figures of the accompanying drawings.